This invention relates generally to fluid handling and more particularly to high pressure fluid pressure regulation.
Dispensing fluids for industrial applications requires accurate control of pressure in order to provide accurate distribution of the fluids in the process. For paints, adhesives, and other high viscosity fluids, distribution pressures of approximately 3,000 psi are frequently required. This has become increasingly true as suppliers of these fluids have minimized the solvent content of these mixtures in response to demands for reduction in health and fire hazards in the workplace. As solvent contents have decreased, the abrasive nature of the suspended solids has become more significant and has begun to adversely affect the service life of the fluid pressure regulators employed in the system.
Typically, a fluid pressure regulator consists of an inlet, an outlet, and a valve placed in the connecting path between the inlet and outlet. A valve closure element is usually biased against the valve seat and is controlled by a stem or other mechanism which is, in turn, adjustably biased counter to the closure element by means of a spring acting on a diaphragm and/or piston which enables the regulator to maintain a constant outlet pressure despite fluctuations in inlet pressure. The piston is adjustably spring biased and is reciprocable within a cylindrical bore in the regulator cover plate. Without a diaphragm, the bore requires a circumferential lip seal in order to prevent leakage of the fluid between the piston and the bore. To function properly against such a seal, the piston requires a very fine finish of the order of 10 microinches or less. Such a finish is expensive to produce and is very easily damaged by corrosion or mechanical injury. Moreover, in the presence of highly abrasive low solvent suspensions, both the seal and the piston finish deteriorate due to sliding contact.
For high pressures, a combination of diaphragm with piston provides more positive sealing. Durability of the diaphragm compared to the lip seal is generally superior since the diaphragm is exposed to flexure rather than sliding wear.
Reduction of solvent content has increased the viscosity of the working materials so that they require higher pumping pressures and, consequently, regulators designed for those pressures. Regulators which were designed to perform in the range of 1000 psi to 1500 psi experienced short service life using the high solids/low solvent materials presently available. Increasing wall thicknesses and spring stiffness alone is not sufficient to upgrade a medium pressure regulator for use in the 3000 psi range of service pressures commonly encountered.
Typically, high pressure regulators employ a diaphragm as well as a piston in a bore of the from cutting, the edges of the piston and the bore of the backup plate are commonly given a radius. The diaphragm commonly consists of fabric mesh reinforced rubber for flexibility and a layer, bonded onto the pumped fluid side, of a chemically resistant material. "O" ring seals are commonly used between the diaphragm, the stem, and the regulator housing.
These features are illustrated in FIG. 1 which presents a cross sectional view of the diaphragm/ piston interfacial area of a typical prior art regulator. The stem 6 and the piston 5 are bolted together to capture the one piece bonded diaphragm 1 and "O" ring seal 7 between them. Diaphragm 1 is composed of fabric reinforced rubber layer 3 and chemical resistant layer 2. Piston 5 reciprocates within bore 8 of backup plate 4. For ease of assembly, chamfer 11 is provided as well as the relatively loose fit between bore 8 and piston 5 which are also radiused as previously described. "O" ring 9 provides a seal between diaphragm 1 and housing 14.
In high pressure surface, this regulator will potentially experience the following problems:
1. the short guide length of the bore between the chamfer and radius on the backup plate can allow the piston to cock slightly within the bore, and can thus permit localized high pressure contact between piston and backup plate and nonuniform flexure of the diaphragm;
2. the large gap, behind the diaphragm, provided by the radii of the backup plate and the piston, allows wedging of the diaphragm into the large gap and consequent excessive abrasion and flexural wear on the diaphragm;
3. the relatively thin backup plate is subject to slight deflection due to high pressure and thus leakage of the working fluid around the seal between the housing and the diaphragm;
4. the one piece bonded diaphragm, because of the different flexural moduli of the two layers, experiences intensified local stresses which cause early failure;
5. in cases where a resonance causes vibration of the piston within the backup plate bore, fretting corrosion may become a significant problem and thus exacerbate the other shortcomings of this design in a high pressure application.
The foregoing illustrates limitations known to exist in present fluid pressure regulators when used in high pressure applications. Thus, it is apparent that it would be advantageous to provide a alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.